The present invention relates to a multilayer wiring substrate suitable for mounting a plurality of electronic circuit elements by a thermocompression bonding technique.
A conventional multilayer wiring substrate using organic materials as dielectric materials which are feasible for finer and denser wiring and smaller capacitance between signal lines has been proposed by Dr. M. Terasawa et al in a paper entitled "A Comparison of Thin Film, Thick Film, and Co-Fired High Density Ceramic Multilayer with The Combined Technology: T&T HDCM", The International Journal for Hybrid Microelectronics, Vol. 6, No. 1 (October 1983), pp. 607-615. The hardness of such organic materials (about 70 to 150 Vickers) is far lower than that of inorganic materials such as alumina (Al.sub.2 O.sub.3) (about 1500 Vickers). For this reason, when wires for connecting to a large-scale integrated circuit (LSI) chip are connected to pads on the substrate by thermocompression bonding under high temperature and pressure, the organic materials are not only caved in or other-wise deformed to prevent adequate bonding but also the underlying wiring layers are disturbed to bring about faulty wiring. The prior art substrate described in the paper, in an attempt to solve the above problem, employs a leadless chip carrier (LCC) through which an LSI chip is connected to the substrate by soldering. However, mounting LSIs to the substrate through LCC's results in a decrease in attainable chip mounting density.